Organopolysiloxane rubber stabilized with tungsten trioxide



United States Patent 3,177,177 ORGAN QPOLYSILOXANE RUBBER STABILHZEDWITH TUNGSTEN TRIGXIDE William J. Bobcat, Latharn, N.Y., assignor toGeneral Electric Company, a corporation of New York No Drawing. Griglnalapplication Apr. 11, 1960, Ser. No. 21,141, now Patent No. 3,898,836,dated July 23, 1963. Divided and this application Oct. 1, 1962, Ser. No.

3 Claims. or. 260-457) This application is a division of my copendingapplication, Serial No. 21,141, filed April 11, 1960, now Patent No.3,098,836, and assigned to the same assignee as the present invention.

The present invention relates to improved organopolysilox'ane rubbercompositions and to a method for making them. More particularly, thepresent invention relates to a method of producing organopolysiloxanerubber compositions having improved heat-age resistance by incorporatingcertain metallic compounds into organopolysiloxanes, and to theresulting rubber compositions produced thereby.

Organopolysiloxane rubber compositions are generally recognized asbeing-more temperature resistant and less subject to decomposition thanthe more conventional types of synthetic-organic or natural rubbers. Aserious problem that has troubled industry is that organopolysiloxanerubber compositions often become brittle and lose many of theirdesirable qualities after extensive use at elevated temperatures.Heat-aging of organopolysiloxane nibber compositions can be reduced byincorporating into the polymer effective amounts of red iron oxideduring the manufacturing stages. As a result, the useful life oforganopolysiloxane rubber compositions has been substantially increased.

While red iron oxide has improved the heat-age resistance oforganopolysiloxane rubber compositions, it has a vivid red color andmust be incorporated into the organopolysiloxane rubber composition inrelatively high amounts to be an effective heat-age additive. As aresult it is virtually impossible to successfully tintorganopolysiloxane rubber compositions containing iron oxide to avariety of attractive shades to improve the appearance of the curedproduct because the red color of the iron oxide is too dominant.

It has now been discovered that by incorporating intoorganopolysiloxanes an effective amount of a-metallic compound in theform of a ertain metal oxide such as tungsten oxide, or nickel oxide,markedly improved readily tintable rubber compositions are produced thatexhibit superior resistance to heat-aging. In addition to enhancing theheat-age resistance of organopolysiloxane causes an alteration in thedesirable physical properties of an organopolysiloxane polymer attemperatures above 150 C. over an extended period of time.

In accordance with the present invention, there are provided oranopolysiloxane rubber compositions having improved resistance toheat-aging comprising (1) 100 .parts of an organopolysiloxaneconvertible to the cured,

solid, elastic state, (2) to 200 parts of a filler, 3) and an effective.amount of a metallic oxide selected from Patent 2,541,137, issuedFebruary 13, 1951.

3,l77,177 Patented Apr. 6, 1965 class of monovalent hydrocarbonradicals, halogenated monovalent hydrocarbon radicals, and cyanoalkylradicals, said organo radicals'being attached to silicon bycarbon-silicon linkages, there being an average of about 1.98 to 2.01organo radicals per silicon atom.

Of the metallic oxides that can be employed in the.

practice of the present invention, tungsten trioxide (W0 is preferred.Tungsten oxide and nickel oxide (NiO) have been found to be eifective inthe range of from about 0.8 to 20 parts by Weight calculated as metal,per parts of organopolysilox'ane polymer, while a preferred range isabout 0.8 to about 8 parts calculated as metal per 100 parts of polymer.

The fibers that are employed in the organopolysiloxane rubbercompositions, are known to the art as reinforcing, and semi-reinforcingfillers. The reinforcing fillers, such as the silica fillers, includingfumed silica, precipitated silica and the like, are structure inducingand depending on their manufacture, may contain or be free of hydroxylgroups either in the form of adsorbed moisture or bonded to siliconatoms. These structure inducing silicone rubber fillers may be modifiedsuch as, for example, by the introduction of silicon-bonded alkoxygroups in place of some hydroxyl groups, resulting in some advantages asdecreased structure when incorporated with a convertibleorganopolysiloxane composition.

The preferred silica filler of the present invention is a fumed silicafiller made by fuming processes including the vapor phase burning ofsilicon tetrachloride or ethylsilicate, an example being what is knownto the trade as Cab-O-Sil. Since a fumed silica contains a relativelylow degree of moisture, it is particularly valuable as a filler additivein organopolysiloxane rubber which is to be used in electricalapplications. Examples of other silica reinforcing fillers may be founddescribed in US. Patents 2,541,137, 2,610,167 and 2,657,149. Suchfillers may be slightly acidic or alkaline (that is, have pHs below orabove 7) depending upon the method of manufacture, such as by an aerogelprocess. Examples of semi-reinforcingor usually non-structure formingtype, are titanium oxide, lithopone, calcium carbonate, iron oxide anddiatomaceous earth. A

Although the convertible organopolysiloxanes employed in the practice ofthe present invention are well known in the art, attention is directedto the convertible organopoly- 'siloxanes disclosed in Agens Patent2,448,756 and Sprung December 28, 1948; Marsden Patent 2,521,528, issuedSeptember 5, 1950all the foregoing patents being assigned to the sameassignee as the present invention; Hyde Patent 2,490,357, issuedDecember 5, 1949; and Warrick It will, of course, be understood by thoseskilled in the art that the convertible organopolysiloxanes referred toherein contain the same or ditterent silicon-bonded organic substituents'(e.g., methyl, ethyl, propyl, vinyl, allyl, phenyl, tolyl,

xylyl, benzyl, phenylethyl, naphthyl, chlorophenyl, cyanoethyl, bothmethyl and phenyl, etc, radicals) connected to the silicon atoms bycarbon-silicon linkages.

The particular convertible organopolysiloxanes used are not critical andmay be any one of those describedin'the foregoing patents. Theymay beviscous masses or gummy solids depending upon the state of condensationof the starting organopolysiloxanes, polymerizing agent, et and may beprepared by condensation'of a liquid organopolysiloxanecontaining anaverage of about 1.95, preferably from about 1.98 to about 2.01 organicgroups per silicon atom. The polymerizing agentsthat can be employed arewell known in the art and can include, for instance, ferric chloridehexahydrate, phenyl phosphoryl chloride; alkaline erally comprises apolymeric diorganosiloxane which can contain, if desired, for example,up to 2 mole percent copolymerized monoorganosiloxane, for example,copoly- Inerize'd.monomethylsiloxane and a small molar (e.g., less than1 mole) percent of triorganosiloxy units, e.g.,

trimethylsiloxy units. Generally, it is preferred to use as l thestarting liquid organopolysiloxanesf(or mixtures of organopolysiloxanes)from which the convertible organopolysiloxanes are prepared, ones whichcontain about 1.999 to 2.01, inclusive, organic groups, for example,methyl groups per silicon atom, and where preferably more than 50percent, 'e.g., more than 75 percent, of the silicon atoms in thepolysiloxane contain two silicon- 1 bonded lower alkyl, e.g., methylgroups.

The starting organopolysiloxanes used to, make the convertibleorganopolysiloxanes advantageously comprise organic constituentsconsisting'essentially of monovalent organic radicals attached tosilicon by carbon-silicon linkages, and in which essentially all of thesiloxane units consist ofunits of the-structural formula R SiO, whereRis preferably a radical of the group consisting of methyl and phenylradicals. At least 50 to 75 percent of the total number of R groups arepreferably methyl radicals. The polysiloxane can be one in which all thesiloxane units are (CH SiO, or the siloxane can be a copolymer ofdimethylsiloxane with a minor amount (e.g., from 1 to or more mole percent) of any of the following units,

separately or mixtures thereof: (C 11 (CH )SiO and (CH H SiO. Thepresence of halogen, e.g., chlorine, atoms on the phenyl nucleus isalsowithin the purview of thepresent invention,

Where alkenyl groups are attached to silicon by carbon-silicon linkages,it is preferable that the alkenyl groups (for instance, vinyl groups,allyl groups, etc.) be present in an amount equal to from 0.05 to 2 molepercent of the total number of silicon-bonded organic groups in theconvertible organopolysiloxane.

Various curing agents to effect more .rapid conversion of theconvertible organopolysiloxane to the cured, solid, elastic state c'anbe incorporated Among such curing agents can be mentioned, for instance,benzoyl peroxide, tertiary butyl perbenzoate, bis-(2,4-dichlorobenzoyl)per oxide, etc. These curing agents (or vulcanization acagent,concentration thereof,the type of polymer, amount of filler, the usedesired,; etc., Persons skilled in the art-will have little difficultyin determining the optimum conditions under various situations involvingditferent temperatures, proportions and ingredients.

In order that those skilled in the art: may, betterunderstand how thepresent invention can be practiced, the following examples are-given bywayof illustration and not by way of limitation." Allparts are byweight.

EXAMPLE 1 A convertible organopolysiloxane within-1 the scope of thepresent invention was made as follows.

Ninety-eight parts by weight of 'o'ctar'nethylcyclotetrasiloxane, ;2parts of' 1,3',5,7-tetrameth'yl-'l,3;5,?7-tetravinylcyclotetrasiloxan'eand0.001 part of potassium'hydroxide were heated at a temperature ofabout 155 C. with agitation for about 4 hours to obtain a highlyviscous, benzene soluble mass of only slight flow.- This convertibleorganopolysiloxane polymer had a viscosity of about 6 millioncentistokes and a ratio of about 1.98 methyl groups, and about 0.02vinyl group per silicon atom.

I One hundred parts of the above convertible organopolysiloxane and 8'parts of diphenylsilanediol were placed in a doughmixer and a mixture ofparts of fumedsilica and 4 parts of tungstenmetal in the form oftungsten trioxide were gradually added. After the formulation was mixedfor 1 hour at 110to 115 C 2 parts of ,benzoyl peroxide was added. Whenthe resulting composition had aged for, 24 hours, itwas milled to asheet. Test strips were then out which were press-cured for 1' hour atlC., and post-cured 24 hours at 250 C. .Additional test strips weremade'following the same procedure that contained 20 parts of tungsten:metal. The. test strips were then heat-aged for an additional 24 hoursat 315 C;

EXAMPLE 2 aged for 24 hours at-315 C.

celerators? as theyv are often designated) can be present in amountsranging from about 0.1'to as high as 4 to 8 percent or more, by weight,based onthe weight of the convertible organopolysiloxane. High energyelectron irradiation without curing agents can also be employed forvulcanizing purposes.

The metallic oxide can be inrorporatcd into theconvertibleorganopolysiloxane. polymer in any desired manner. It is preferred toadd the metallic oxide to the polymer in finely divided form such asto aparticle size in the range .0f'50' microns or below to avoid modifyingthe properties 'desired inthe final cured rubber product. The metallicoxide-can be added directly into-the organopolys iloxane polymer, intothe. polymer and filler mixture or, if desired, can beadded along withthefiller into the polymer.

It is advisable to add the metallic oxide to theorganopoly siloxaneprior to the addition of the .curing catalyst to avoid undersirable sideeffects and to achieve optimum results. a

, Addition of a suitable curing catalyst can be preformed V at, anystageof the processing but it is preferred to add it after mixing'theorganopolysiloxane polymer with :the filler and the metallic .oxide.Thereafter, the composibe employed in combination with temperaturesranging from about 80- C. to 200,C. or higher. Under v such a tion canbef'molded'or used many. application desired.

conditions, the time required for effecting the desired:

:cure will depend upon such factors as the type of curing Control stripswere also made in accordance Withthe above procedure, that co'ntained5parts'of red iron oxide perfilOO parts of organopolysiloxanepolymer. 'Inaddition, .control strips were made that were free of a heatageadditive. V

The test strips werepres's-cured and conditioned for 24 hours at 25 0:C., and then measured in accordance with A.S.T.M. specifications asshown in the 1 table below- Hardness "H (Shore A), tensile strength T(p.s.i.), and elongation E (percent), were'determined. After initialmeasurements were taken, the test strips. were subjected-to .anadditional heat treatment by placingthem in an oven for 24 hours atabout 315 C." Measurements were again taken to determine whether theproperties of the strips were altered-due to thepossible effects'ofheataging. Theparts by'weight of metallic oxide in the table areexpressed in terms of parts by weight of metal per 7 parts oforganopolysiloxane polymer.

T able Quad J Heat-Aged 24-Hrs/250O 24'Hrs/315C HeabAge Additive Parts 7in. ;'r E. .11" T. E

None 56 938 310" Iron Oxide. 5 56 838 310 1 7 l' 570 Tungsten Oxide 4. 055 1, 013 300 60 630 270 DOLL 20.0 v p 57 670' 250 72 490 100 1 Toobrittle to test. I I, The above table clearly showsthe effectiveness of,the

substantially color-free metal oxides of thepresent inven m in mp r ingimproved heat-age resistance, to" organopolysiloxane rubber compositionsascompared to red iron a oxide. The samples prepared in accordance withExample 2, employing nickel oxide were also found to have substantiallyimproved resistance to heat-aging as compared to the sample containingno heat-age additive.

While the foregoing examples have of necessity been limited to only afew of the very many variables Within the scope of thepresent invention,it should be understood that the present invention covers a much broaderclass of organopolysiloxane compositions containing the metal oxidesincluded within the scope of the present invention. All of these variousmaterials are prepared by methods specifically illustrated in theexamples above and described further in the foregoing description of thepresent invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A process for producing an organopolysiloxane rubber compositionhaving improved resistance to heat-aging comprising mixing together byweight, (1) 0.8 to 20 parts of tungstein metal in the form of an oxideof tungsten consisting essentially of tungsten trioxide, (2) 100 partsof an organopolysiloxane, (3) to 200 parts of a filler, (4) and a curingcatalyst, and curing the resulting composition at temperatures in therange of 80 to 200 C., said organopolysiloxane having a viscosity of atleast 100,000 centipoises when measured at 25 C., the organo radicals ofsaid organopolysiloxane being members selected from the class consistingof monovalent hydrocarbon radicals, halogenated monovalent hydrocarbonradicals, and cyanoalkyl radicals, there being an average of about 1.98to 2.0101- gano radicals per silicon atom.

2. Organopolysiloxane compositions comprising by weight, (1) parts of anorganopolysiloxane, (2) 10 to 200 parts of a filler, and (3) 0.8 to 20parts of tungsten metal in the form of an oxide of tungsten consistingessentially of tungsten trioxide, said organopolysiloxane having aviscosity of at least 100,000 centipoises when measured at 25 C., theorgano radicals of said organopolysiloxane being members selected fromthe class consisting of monovalent hydrocarbon radicals, halogenatedmonovalent hydrocarbon radicals and cyanoalkyl radicals, there being anaverage of about 1.98 to 2.01 organo radicals per silicon atom.

3. A composition in accordance with claim 2 containing about 4- parts oftungsten metal in the form of tungsten trioxide.

References @ited by the Examiner UNITED STATES PATENTS OTHER REFERENCESSilicone Rubber, Its Growth and Recent Developments (Servais et al.),The Rubber and Plastics Age, vol.

38, pages 600-608 (July 1957).

MORRIS LIEBMAN, Primary Examiner. ALEXANDER H. BRODMERKEL, Examiner.

1. A PROCESS FOR PRODUCING AN ORGANOPOLYSILOXANE RUBBER COMPOSITIONHAVING IMPROVED RESISTANCE TO HEAT-AGING COMPRISING MIXING TOGETHER BYWEIGHT, (1) 0.8 TO 20 PARTS OF TUNGSTEIN METAL IN THE FORM OF AN OXIDEOF TUNGSTEN CONSISTING ESSENTIALLY OF TUNGSTEN TRIOXIDE, (2) 100 PARTSOF AN ORGANOPOLYSILOXANE, (3) 10 TO 100 PARTS OF A FILLER, (4) AND ACURING CATALYST, AND CURING THE RESULTING COMPOSITION AT TEMPERATURES INTHE RANGE OF 80 TO 200%C., SAID ORGANOPOLYSILOXANE HAVING A VISCOSITY OFAT LEAST 100,000 CENTIPOISES WHEN MEASURED AT 25*C., THE ORGANO RADICALSOF SAID ORGANOPOLYSILOXANE BEING MEMBERS SELECTED FROM THE CLASSCONSISTING OF MONOVALENT HYDROCARBON RADICALS, HALOGENATED MONOVALENTHYDROCARBON RADICALS, AND CYANOALKYL RADICALS, THERE BEING AN AVERAGE OFABOUT 1.98 TO 2.01 ORGANO RADICALS PER SILICON ATOM.